R2511-HP MSR Router Series High Availability Configuration Guide(V5)

How interface backup works

Interface backup operates in active/standby mode or in load balancing mode.

Active/standby mode

As shown in Figure 5, interface Serial 2/0 on Router A acts as the active interface and interfaces Serial

2/1 and Serial 2/2 act as the standby interfaces.

Figure 5 Diagram for active/standby mode

In active/standby mode, only one interface transmits data at any given time.

• When the active interface is operating correctly, even if the traffic is overloaded, the standby

interface is in a backup state. All traffic is transmitted by the active interface.

• If the active interface fails, the standby interface with highest priority takes over to transmit data.

• When the active interface is restored, it resumes data transmission.

Load balancing mode

As shown in Figure 6, interface Serial 2/0 on Router A acts as the active interface, and interfaces Serial

2/1 and Serial 2/2 act as the standby interfaces.

Figure 6 Diagram for load balancing mode

In load balancing mode, you can set an upper threshold (enable-threshold) and a lower threshold

(disable-threshold). Traffic can be shared among multiple interfaces:

• When the traffic on the active interface exceeds the predefined enable-threshold, the highest

priority standby interface is activated. Other standby interfaces are activated in descending priority

order if exceeding traffic still exists.

• When the traffic on the active interface decreases below the predefined disable-threshold, the

system shuts down the lowest priority standby interface first and then shuts down the other standby

interfaces in ascending priority order depending on traffic size.